This invention relates to filters and in the more important example to microporous filters capable of separating micron sized particles such as microorganisms and ultrafiltration membranes capable of retaining macromolecules such as proteins. The invention also relates to methods of filtering.
Filters are presently constructed of polymers (such as cellulose derivatives, teflon and nylon), ceramics, metals (for example stainless steel) and metal oxides (for example aluminium). It has been proposed (see U.S. Pat. No. 4,279,751) to produce a hydraulic fluid filter element which comprises a body of porous piezoelectric material. An alternating voltage is supplied to metallized surfaces of the body to effect vibration, thereby reducing clogging of the filter and promoting the breakdown of contaminants in the hydraulic fluid.